We have investigated the biochemical mechanism for the regulation of triacylglycerol and glycerophospholipid metabolism associated with the absorptive process by the intestinal mucosal tissue. Employing the ether analogs of monoacylglycerol we have demonstrated the specific inhibition of glycero-3-phosphate acylation. We have developed a HPLC method for the separation of cytidine mono-, di-, triphosphates, and CDP-choline. Preliminary experiments would suggest that glycerophospholipid biosynthesis may be regulated by the intracellular concentrations of these cytidine derivatives. Phosphohydrolase activity is closely associated with the lamellar bodies isolated from lung tissue. A mechanism has been proposed for the regulation of phosphatidyl-choline, -inositol and -glycerol biosynthesis as their concentrations are found in the mature surfactant. Support for this postulate has been obtained by the demonstration that the CMP concentration of fetal rabbit lung increases as a function of gestational age.